The invention relates to a control apparatus for internal combustion engines.
Known control apparatuses of this kind (German laid-open applications Nos. 24 48 656 and 24 32 830) function in accordance with the absolute pressure of the aspirated air in the suction tube of the engine; in aspirating engines, that is, they function in accordance with atmospheric pressure, and in supercharged engines they function in accordance with the charge air pressure. Because of the limited work capacity of the diaphragm pressure boxes which process the absolute pressure of the aspirated air, the adjusting member of this apparatus, having a movable wall, is preceded by a control device, in which the position of a valve member for controlling a servo pressure medium is determined by an evacuated diaphragm pressure box exposed to the aspirated air pressure. This control device functions as a hydraulic follower-piston unit, and the diaphragm pressure box must generate either a control path corresponding to the required adjusting-member path for twisting an adjuster eccentric or, in the case of the German laid-open application No. 25 32 830, a control path such as is required for displacing a three-dimensional cam. This sometimes requires relatively long adjustment paths, which involve friction, and thus also necessitates correspondingly large diaphragm box sets. Furthermore, the supply and sealing of the structural elements exposed to the hydraulic medium represents a relatively great expense.
Other known control apparatuses, which functions without a servo medium and include adjustment members directly exposed to the diaphragm pressure boxes, likewise have much too little work capacity, and the necessary adjustment paths are difficult to attain. Control apparatuses are also known whose diaphragm adjustment members, exposed directly to the charge air pressure, by contrast do have a larger work capacity; however, they work only with the differential pressure between the charge air pressure and atmospheric pressure and cannot furnish any absolute pressure signal such as is required in order to prevent impermissible smoke generation, especially when the engine is operated in areas of extreme variations in altitude.
The adjustment members of the known control apparatuses either engage the governor linkage, in order to adapt the governor characteristic in accordance with the varying absolute pressure of the aspirated air, or, acting as a full-load stop, they limit the particular permissible full-load position of a supply quantity adjustment member of the fuel metering apparatus.